Using C++¶

Lecture 11 will cover the baiscs of C++ progamming.
Lecture 12 will cover how to call C++ libraries from Python using pybind11

Since we are mainly learning C++ to wrap for use in Python, we will ignore C++ I/O.

The compilation process¶

Compilation process

Hello, world¶

%mkdir hello
%cd hello

mkdir: hello: File exists
/Users/cliburn/git-teach/sta-663-2017-public/scratch/hello

%%file hello.cpp

#include <iostream>
using std::cout;
using std::endl;

int main() {
    cout << "Hello, world" << endl;
}

Overwriting hello.cpp

! g++ hello.cpp -o hello

! ./hello

Hello, world

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public/scratch

A simple function¶

%mkdir add1
%cd add1

mkdir: add1: File exists
/Users/cliburn/git-teach/sta-663-2017-public/scratch/add1

%%file add.cpp

#include <iostream>
using std::cout;
using std::endl;

double add(double a, double b) {
    return a + b;
}

int main() {
    double a = 1.0, b= 2.0;

    double c = add(a, b);

    cout << a << " + " << b << " = " << c << endl;
}

Overwriting add.cpp

! g++ add.cpp -o add

! ./add

1 + 2 = 3

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public/scratch

Using header files¶

%mkdir add2
%cd add2

mkdir: add2: File exists
/Users/cliburn/git-teach/sta-663-2017-public/scratch/add2

%%file add.hpp

#pragma once
double add(double a, double b);

Overwriting add.hpp

%%file add.cpp

double add(double a, double b) {
    return a + b;
}

Overwriting add.cpp

%%file add_driver.cpp

#include "add.hpp"
#include <iostream>
using std::cout;
using std::endl;

int main() {
    double a = 1.0, b = 2.0;

    double c = add(a, b);

    cout << a << " + " << b  << " = " << c << endl;
}

Overwriting add_driver.cpp

%%bash

g++ add_driver.cpp add.cpp -o add_driver
./add_driver

1 + 2 = 3

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public/scratch

Notes:¶

#pragma once is non-standard but very widely supported
if you want to be pedantic, use traditional guards

%%file src/add.hpp

#ifndef ADD_HPP
#define ADD_HPP
double add(double a, double b);
#endif /* ADD_HPP */

Using `make`¶

%mkdir add3
%cp add2/add.cpp add2/add.hpp add2/add_driver.cpp add3/
%cd add3

mkdir: add3: File exists
/Users/cliburn/git-teach/sta-663-2017-public/scratch/add3

%%file Makefile

add_driver: add_driver.o add.o
    g++ add_driver.o add.o -o add_driver

add_driver.o: add_driver.cpp add.hpp
    g++ -c add_driver.cpp

add.o: add.cpp
    g++ -c add.cpp

.PHONY: clean
clean:
    rm add_driver *.o

Overwriting Makefile

! make

g++ -c add_driver.cpp
g++ -c add.cpp
g++ add_driver.o add.o -o add_driver

! make clean

rm add_driver *.o

! make

g++ -c add_driver.cpp
g++ -c add.cpp
g++ add_driver.o add.o -o add_driver

A reusable Makefile¶

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = add_driver
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make clean
make
./add_driver

rm -f add_driver add.o add_driver.o
g++ -c -Wall -std=c++11 add.cpp -o add.o
g++ -c -Wall -std=c++11 add_driver.cpp -o add_driver.o
g++ add.o add_driver.o -o add_driver
1 + 2 = 3

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public/scratch

Linking to a library¶

%mkdir linker
%cd linker

mkdir: linker: File exists
/Users/cliburn/git-teach/sta-663-2017-public/scratch/linker

%%file test_linker.cpp

#include <cmath>
#include <iostream>
using std::cout;
using std::endl;

int main() {
    cout << "2^10 = " << pow(2, 10) << endl;
}

Overwriting test_linker.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = test_linker
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

! make

g++ -c -Wall -std=c++11 test_linker.cpp -o test_linker.o
g++ test_linker.o -o test_linker

! ./test_linker

2^10 = 1024

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public/scratch

Arrays, pointers and dereferencing¶

%mkdir arrays
%cd arrays

mkdir: arrays: File exists
[Errno 20] Not a directory: 'arrays'
/Users/cliburn/git-teach/sta-663-2017-public/scratch

%%file arrays.cpp

#include <cmath>
#include <iostream>
using std::cout;
using std::endl;

int main() {

    // pointers and address-of opertor
    int a = 1, b = 2;
    int *p = &a, *q = &b;

    cout << a << ", " << b << endl;
    cout << *p << ", " << *q << endl;
    cout << p << ", " << q << endl;

    // An array name is just a pointer
    int ms[] = {1,2,3,4};

    // using indexing
    cout << ms[0] << ", " << ms[1] << endl;
    // using pointer arithmetic
    cout << *(ms) << ", " << *(ms + 0) << ", " << *(ms + 2) << endl;
    cout << 2[ms] << ", " << 3[ms] << endl; // wait, what??

    // size of an array
    cout << sizeof(ms)/sizeof(*ms) << endl;
}

Overwriting arrays.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = arrays
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make
./arrays

g++ -c -Wall -std=c++11 arrays.cpp -o arrays.o
g++ arrays.o -o arrays
1, 2
1, 2
0x7fff56a6b4fc, 0x7fff56a6b4f8
1, 2
1, 1, 3
3, 4
4

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public

Loops in C++¶

%mkdir loops
%cd loops

mkdir: loops: File exists
/Users/cliburn/git-teach/sta-663-2017-public/loops

%%file loops.cpp

#include <cmath>
#include <iostream>
using std::cout;
using std::endl;

int main() {
    double xs[] = {0,1,2,3,4,5,6,7,8,9};

    // looping with an index
    for (int i=0; i<sizeof(xs)/sizeof(*xs); i++) {
        cout << pow(xs[i], 2) << " ";
    }
    cout << endl;

    // looping with an iterator
    for (auto it=std::begin(xs); it!=std::end(xs); it++) {
        cout << pow(*it, 2) << " ";
    }
    cout << endl;

    // ranged for loop
    for (auto x : xs) {
        cout << pow(x, 2) << " ";
    }
    cout << endl;

}

Overwriting loops.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = loops
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make clean
make
./loops

rm -f loops loops.o
g++ -c -Wall -std=c++11 loops.cpp -o loops.o
g++ loops.o -o loops
0 1 4 9 16 25 36 49 64 81
0 1 4 9 16 25 36 49 64 81
0 1 4 9 16 25 36 49 64 81

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public

Functions in C++¶

%mkdir funcs1
%cd funcs1

mkdir: funcs1: File exists
/Users/cliburn/git-teach/sta-663-2017-public/funcs1

%%file funcs1.cpp

#include <iostream>
using std::cout;
using std::endl;

double sum(double *xs, int n) {
    double s = 0.0;

    for (int i=0; i<n; i++) {
        s += xs[i];
    }
    return s;
}

void triple(double *xs, double * ys, int n) {
     for (int i=0; i<n; i++) {
        ys[i] = 3 * xs[i];
    }
}

int main() {
    double xs[] = {1,2,3,4};
    int n = sizeof(xs)/sizeof(*xs);

    cout << sum(xs, n) << endl;

    double ys[n];

    triple(xs, ys, n);
        for (auto y : ys) {
        cout << y << " ";
    }
    cout << endl;
}

Overwriting funcs1.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = funcs1
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make
./funcs1

g++ -c -Wall -std=c++11 funcs1.cpp -o funcs1.o
g++ funcs1.o -o funcs1
10
3 6 9 12

%cd ..

/Users/cliburn/git-teach/sta-663-2017-public

Anonymous functions¶

%mkdir funcs2
%cd funcs2

mkdir: funcs2: File exists
[Errno 20] Not a directory: 'funcs2'
/Users/cliburn/git-teach/sta-663-2017-public

%%file funcs2.cpp

#include <iostream>
using std::cout;
using std::endl;

int main() {
    double k = 5.0;
    double a = 1.0, b = 2.0;

    auto add1 = [](int a, int b) { return a + b; };
    auto add2 = [k](int a, int b) { return a + b + k; };
    auto add3 = [&k](int a, int b) { return a + b + k; };

    k *= 2;

    cout << "Lambda: " << add1(a, b) << endl;
    cout << "Lambda with capture by value: " << add2(a, b) << endl;
    cout << "Lmabda with capture by reference: " << add3(a, b) << endl;
}

Overwriting funcs2.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = funcs2
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make clean
make
./funcs2

rm -f funcs2 funcs2.o
g++ -c -Wall -std=c++11 funcs2.cpp -o funcs2.o
g++ funcs2.o -o funcs2
Lambda: 3
Lambda with capture by value: 8
Lmabda with capture by reference: 13

%cd ..

/Users/cliburn/git-teach

Templates¶

%mkdir templates
%cd templates

mkdir: templates: File exists
/Users/cliburn/git-teach/templates

%%file templates.cpp

#include <iostream>
#include <vector>
#include <list>
#include <numeric>
using std::cout;
using std::endl;
using std::list;
using std::vector;

template<typename T>
T sum(vector<T> xs) {
    T s = 0.0;
    for (auto x : xs) {
        s += x;
    }
    return s;
}

int main(){
    vector<int> ns = {1,2,3};
    vector<double> xs = {4.5, 6.4, 7.8};

    // sum works with integers
    cout << "Sum of ints: " << sum(ns) << endl;

    // sum works with doubles
    cout << "Sum of doubles: " << sum(xs) << endl;

    // iota from the numeric library behaves like range
    list<int> ys(10);
    std::iota(ys.begin(), ys.end(), -3);

    // accumulate from the numeric library behavses like reduce with default operation of addition
    cout << "Sum from iota: " << std::accumulate(ys.begin(), ys.end(), 6.0) << endl;

    // Note that the initial value determines the template type
    cout << "Sum of doubles using accumulate: " << std::accumulate(xs.begin(), xs.end(), 0.0) << endl;
    cout << "Surpise: " << std::accumulate(xs.begin(), xs.end(), 0) << endl;


    // The binary operation can be user-defined
    auto op = std::multiplies<int>();
    cout << "Product of ints: " << std::accumulate(ns.begin(), ns.end(), 1, op) << endl;
}

Overwriting templates.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = templates
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make clean
make
./templates

rm -f templates templates.o
g++ -c -Wall -std=c++11 templates.cpp -o templates.o
g++ templates.o -o templates
Sum of ints: 6
Sum of doubles: 18.7
Sum from iota: 21
Sum of doubles using accumulate: 18.7
Surpise: 17
Product of ints: 6

%cd ..

/Users/cliburn/git-teach

Function pointers¶

%mkdir func_ptrs
%cd func_ptrs

mkdir: func_ptrs: File exists
/Users/cliburn/git-teach/func_ptrs

%%file func_ptrs.cpp

#include <numeric>
#include <functional>
#include <iostream>
#include <vector>
using std::cout;
using std::endl;
using std::vector;

double sum(vector<double> xs) {
    return std::accumulate(xs.begin(), xs.end(), 0.0);
}

double prod(vector<double> xs) {
    return std::accumulate(xs.begin(), xs.end(), 1.0, std::multiplies<double>());
}

// funciton pointers in C++ are easy
using func = std::function<double(double)>;

// now you can pass in a funciton as an argument
double mystery(double x, func f) {
    return f(x);
}

double foo(double x) {
    return 2*x + 1;
}

double bar(double x) {
    return 42*x;
}

int main() {
    vector<double> xs = {1.2, 2.3};
    cout << sum(xs) << endl;
    cout << prod(xs) << endl;

    // auto can crate iterables of functions!
    auto funcs = {sum, prod};
    for (auto f: funcs) {
        cout << f(xs) << endl;
    }

    int x = 2;
    cout << mystery(x, foo) << endl;
    cout << mystery(x, bar) << endl;
    cout << mystery(x, [](double x) {return x*x;}) << endl;

}

Overwriting func_ptrs.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11

# File names
EXEC = func_ptrs
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make clean
make
./func_ptrs

rm -f func_ptrs func_ptrs.o
g++ -c -Wall -std=c++11 func_ptrs.cpp -o func_ptrs.o
g++ func_ptrs.o -o func_ptrs
3.5
2.76
3.5
2.76
5
84
4

%cd ..

/Users/cliburn/git-teach

Using a numeric library¶

We show the Armadillo numeric library here; in the next lecture, we will show the competing Eigen libary.

%mkdir numeric
%cd numeric

mkdir: numeric: File exists
/Users/cliburn/git-teach/numeric

%%file numeric.cpp

#include <iostream>
#include <fstream>
#include <armadillo>
using std::cout;
using std::ofstream;

int main()
{
    using namespace arma;

    vec u = linspace<vec>(0,1,5);
    vec v = ones<vec>(5);
    mat A = randu<mat>(4,5); // uniform random deviates
    mat B = randn<mat>(4,5); // normal random deviates

    cout << "\nVecotrs in Armadillo\n";
    cout << u << endl;
    cout << v << endl;
    cout << u.t() * v << endl;

    cout << "\nRandom matrices in Armadillo\n";
    cout << A << endl;
    cout << B << endl;
    cout << A * B.t() << endl;
    cout << A * v << endl;

    cout << "\nQR in Armadillo\n";
    mat Q, R;
    qr(Q, R, A.t() * A);
    cout << Q << endl;
    cout << R << endl;
}

Overwriting numeric.cpp

%%file Makefile
# Declaration of variables
CC = g++
CC_FLAGS = -Wall -std=c++11
LD_FLAGS = -larmadillo # Add library for linking

# File names
EXEC = numeric
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

# Main target
$(EXEC): $(OBJECTS)
    $(CC) $(LD_FLAGS) $(OBJECTS) -o $(EXEC)

# To obtain object files
%.o: %.cpp
    $(CC) -c $(CC_FLAGS) $< -o $@

# To remove generated files
clean:
    rm -f $(EXEC) $(OBJECTS)

Overwriting Makefile

%%bash

make clean
make
./numeric

rm -f numeric numeric.o
g++ -c -Wall -std=c++11 numeric.cpp -o numeric.o
g++ -larmadillo  numeric.o -o numeric

Vecotrs in Armadillo
        0
   0.2500
   0.5000
   0.7500
   1.0000

   1.0000
   1.0000
   1.0000
   1.0000
   1.0000

   2.5000


Random matrices in Armadillo
   7.8264e-06   5.3277e-01   6.7930e-01   8.3097e-01   6.7115e-01
   1.3154e-01   2.1896e-01   9.3469e-01   3.4572e-02   7.6982e-03
   7.5561e-01   4.7045e-02   3.8350e-01   5.3462e-02   3.8342e-01
   4.5865e-01   6.7886e-01   5.1942e-01   5.2970e-01   6.6842e-02

  -0.7649   1.2041  -0.7020   1.1862   0.8284
   1.7313   0.0937   1.6814  -0.8631   0.9426
   0.1454  -0.6920   0.2742   0.6810   0.2091
   0.7032   0.2610   0.1752   1.3165  -0.5897

   1.7063   1.1075   0.5238   0.9563
  -0.4457   1.7973   0.1490   0.3544
  -0.4095   2.2726   0.2990   0.4551
   0.7857   1.3368   0.1140   1.2487

   2.7142
   1.3275
   1.6230
   2.2535


QR in Armadillo
  -0.6776   0.6377   0.3253   0.0944  -0.1395
  -0.3188  -0.4409   0.3521   0.4177   0.6368
  -0.5524  -0.2366  -0.7774   0.1504  -0.1092
  -0.2443  -0.5816   0.4071  -0.1709  -0.6380
  -0.2727  -0.0688  -0.0099  -0.8745   0.3950

  -1.1785e+00  -1.3394e+00  -2.1015e+00  -1.3527e+00  -1.0229e+00
        0e+00  -8.3421e-01  -9.7607e-01  -9.9515e-01  -5.3245e-01
        0e+00        0e+00  -4.6336e-01   7.6793e-02  -4.0376e-03
        0e+00        0e+00        0e+00  -2.0273e-01  -3.2745e-01
        0e+00        0e+00        0e+00        0e+00   1.1102e-16

%cd ..

/Users/cliburn/git-teach

Using C++¶

The compilation process¶

Hello, world¶

A simple function¶

Using header files¶

Notes:¶

Using `make`¶

A reusable Makefile¶

Linking to a library¶

Arrays, pointers and dereferencing¶

Loops in C++¶

Functions in C++¶

Anonymous functions¶

Templates¶

Function pointers¶

Using a numeric library¶

Table Of Contents

Previous page

Next page

This Page

Using C++¶

The compilation process¶

Hello, world¶

A simple function¶

Using header files¶

Notes:¶

Using make¶

A reusable Makefile¶

Linking to a library¶

Arrays, pointers and dereferencing¶

Loops in C++¶

Functions in C++¶

Anonymous functions¶

Templates¶

Function pointers¶

Using a numeric library¶

Using `make`¶